under
some (but not unusual) circumstances, there will be no threshold
level below which there is no effect, and

contaminants
exposures take place in mixtures and these mixtures can interact
additively, synergistically or not at all.

These
four aspects of endocrine disruption challenge fundamental elements
of how risk assessment is currently practiced in the United States
(and most other countries). They mean that the current
protective structure used to protect people from contaminants in
the United States are fundamentally flawed.

The
levels of contamination
known to cause effects are dramatically lower than current testing
procedures examine. New data examining hormonal effects
of bisphenol A, for example, suggest federal tolerances should be
at least 25,000 times lower than current approaches would determine.

Endocrine
disrupting chemicals violate
a basic assumption of toxicology and modern risk assessment.
For classic toxicants, "the dose makes the poison."
As the dose increases so too does the effect. Dose - response is understood
as a linear relationship. For some endocrine disrupting chemicals,
however, effects may disappear at higher levels, or become different
qualitatively, and may appear at levels below the no observable adverse
effect level, or NOAEL. This means that high dose testing, the
standard procedure of risk assessment, cannot reveal the health risks
posed by endocrine disrupters. And that means that most toxicological
tests done for most regulatory decisions must be repeated at environmentally-relevant
(i.e., much lower) levels. In the meantime, this means the US
EPA, FDA, and industry are utterly lacking in scientific guidance
for regulatory decisions about endocrine disrupters.

Traditional
toxicology often assumes that there is some level of exposure, a
threshold, beneath which small amounts of a contaminant have no
effect.New
research has demonstrated that endocrine disrupting compounds violate
this assumption, that there is literally no
threshold of effect for an endocrine disrupting compound
when it is added to a hormone system that is already active. The
crucial point is that traditional toxicants are thought to work
by starting a process (or stopping one) by overwhelming the body's
defense system. Up to some level of contamination, the body can
defend itself against chemical assaults. Endocrine disrupting chemicals,
in contrast, are adding to or subtracting from chemical signals
that are directing processes already underway.

No
one is exposed to just one chemical. Our exposures come
in mixtures whose compositions depend upon our life style, where we
live, our age and many other factors. Most research on the health
impacts of contamination tests compounds one chemical at a time and
thus are extreme simplifications of the real world. Results
emerging from research labs that test the combined effects of different
chemicals are revealing complex interactions... sometimes additive,
sometimes synergistic, and sometimes a canceling effect.
Even these experiments, the most complicated of which rarely involve
more than a few chemicals simultaneously, pale in comparison with
the uncontrolled "experiments" that are taking place in
humans and wildlife today; as typical exposures involve several hundred
chemicals simultaneously.